Seat reclining mechanism

ABSTRACT

Disclosed is a seat reclining mechanism, which is designed to be mounted to a seat cushion and a seat back so as to allow the seat back to be reclined. The seat reclining mechanism comprises a guide bracket and an internal gear member coupled to the guide bracket in a rotatable manner about a rotation axis thereof with respect to the guide bracket and formed with internal teeth along a circle having a center on the rotation axis. A plurality of lock gear members is disposed between the guide bracket and the internal gear member. A fitting portion is provided in either one of the guide bracket and the internal gear member. A rotatable cam is rotatably supported by the fitting portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a seat reclining mechanism.

2. Description of the Related Art

Heretofore, there has been known a seat reclining mechanism designed tobe mounted to a seat cushion and a seat back so as to allow the seatback to be reclined. JP 2001-017259A and JP 2004-154585A disclose areclining mechanism which comprises a guide bracket adapted to bemounted to either one of a seat cushion and a seat back, an internalgear member (i.e., internally-toothed gear member) adapted to be mountedto a remaining one of the seat cushion and the seat back, a plurality oflock gear members disposed between the guide bracket and the internalgear member and adapted to be slidingly guided in a radial direction, arotatable cam adapted to move the lock gear members in both a lockdirection causing the lock gear members to be brought into engagementwith the internal gear member and an unlock direction causing the lockgear members to be released from the engagement with the internal gearmember, and a lock spring biasing the rotatable cam in a lock-causingrotation direction.

In this mechanism, when an operator operates an operation lever torotate the rotatable cam in a direction opposite to the lock-causingrotation direction, the lock gear members are moved in the unlockdirection through a circular lever (actuating plate), and released fromthe engagement with the internal gear member. Thus, the seat back can beforwardly or rearwardly inclined. Then, when the operator releaseshis/her hand from the operation lever, the rotatable cam is rotated inthe lock-causing rotation direction by a biasing force of the lockspring, and the lock gear members are moved in the lock direction andbrought into engagement with the internal gear member. Thus, the seatback is locked at an intended inclined position.

In the above mechanism, if a center of the rotatable cam is displacedfrom a normal position due to the biasing force of the lock spring, thelock gear members are likely to become unable to be evenly moved, whichleads to instability in lock function of the lock gear members.

For this reason, the rotatable cam is integrated with an operationmember, such as an operation rod connected to the operation lever, andthe operation member supported by a bearing member, such as a knucklebracket, provided outside the reclining mechanism, so as to performcentering of the rotatable cam.

However, in the structure designed to support the operation member bythe bearing member, such as a knuckle bracket, the operation member andthe bearing member have to be prepared with a high degree of dimensionalaccuracy to cause a problem about an increase in cost.

SUMMARY OF THE INVENTION

In view of the above problem, it is an object of the present inventionto provide a low-cost seat reclining mechanism.

In order to achieve this object, the present invention provides a seatreclining mechanism designed to be mounted to a seat cushion and a seatback so as to allow the seat back to be reclined. The seat recliningmechanism comprises: a guide bracket adapted to be mounted to either oneof the seat cushion and the seat back; an internal gear member adaptedto be mounted to a remaining one of the seat cushion and the seat back,wherein the internal gear member is coupled to the guide bracket in arotatable manner about a rotation axis thereof with respect to the guidebracket, and formed with internal teeth along a circle having a centeron the rotation axis; a plurality of lock gear members disposed betweenthe guide bracket and the internal gear member to extend radially fromthe rotation axis, wherein each of the lock gear members is formed withexternal teeth meshingly engageable with the internal teeth, andsupported by the guide bracket in such a manner as to be slidable inboth a lock direction causing the external teeth to be brought intomeshing engagement with the internal teeth and an unlock directioncausing the external teeth to be released from the meshing engagementwith the internal teeth; a fitting portion provided in either one of theguide bracket and the internal gear member; a rotatable cam rotatablysupported by the fitting portion, and adapted to be rotatable in both alock-causing rotation direction causing the lock gear members to beslidingly moved in the lock direction and an unlock-causing rotationdirection causing the lock gear members to be slidingly moved in theunlock direction; and a lock spring biasing the rotatable cam in thelock-causing rotation direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a reclining mechanismaccording to one embodiment of the present invention.

FIG. 2A is a sectional view showing the mechanism, taken along the lineIIA-IIA in FIG. 2B.

FIG. 2B is a see-through front view showing the mechanism, when viewedfrom the side of an internal gear member.

FIG. 3A is a front view of a guide bracket in the mechanism, when viewedfrom the side of an inner surface thereof.

FIG. 3B is a back view showing the guide bracket, when viewed from theside of an outer surface thereof.

FIG. 4A is a front view showing the internal gear member in themechanism, when viewed from the side of an inner surface thereof.

FIG. 4B is a back view showing the internal gear member, when viewedfrom the side of an outer surface thereof.

FIG. 5A is a front view showing a lock gear member having a protrusion,which is one of a plurality of lock gear members in the mechanism.

FIG. 5B is a front view showing a lock gear member devoid of theprotrusion, which is one of the plurality of lock gear members.

FIG. 5C is a front view showing a rotatable cam in the mechanism.

FIG. 6A is a see-through front view showing the mechanism, when viewedfrom the side of the internal gear member, in a state after a seat backis set at an initial locked position.

FIG. 6B is a see-through front view showing the mechanism, when viewedfrom the side of the internal gear member, wherein the protrusion islocated on a free-zone arc portion.

FIG. 7A is a see-through front view showing the mechanism, when viewedfrom the side of the internal gear member, wherein aforwardmost-inclination stopper portion is in contact with aforwardmost-inclination stopper protrusion.

FIG. 7B is a see-through front view showing the mechanism, when viewedfrom the side of the internal gear member, wherein arearwardmost-inclination stopper portion is in contact with arearwardmost-inclination stopper protrusion.

FIG. 8A is a see-through front view showing a reclining mechanism of atype designed to lock a seat back at a forwardmost inclined position,when viewed from the side of an internal gear member, in a state whenthe seat back is locked at the forwardmost inclined position.

FIG. 8B is a see-through front view showing the mechanism in FIG. 8A,when viewed from the side of the internal gear member, in a state whenthe seat back is locked at an initial locked position, e.g., an uprightposition.

FIG. 9A is a see-through front view showing a reclining mechanism of atype designed to keep a seat back from being locked at a forwardmostinclined position, when viewed from the side of an internal gear member,in a state when the seat back is set at the forwardmost inclinedposition without being locked.

FIG. 9B is a see-through front view showing the mechanism in FIG. 9A,when viewed from the side of an internal gear member, in a state whenthe seat back is locked at an initial locked position, e.g., an uprightposition.

FIG. 10 is a local front view showing a reclining mechanism as a firstmodification of the embodiment illustrated in FIG. 1

FIG. 11A is a sectional view showing a reclining mechanism as a secondmodification of the embodiment illustrated in FIG. 1, taken along theline XIA-XIA in FIG. 11B.

FIG. 11B is a see-through front view showing the mechanism as the secondmodification, when viewed from the side of an internal gear member.

FIG. 12A is a sectional view showing a reclining mechanism as a thirdmodification of the embodiment illustrated in FIG. 1, taken along theline XIIA-XIIA in FIG. 12B.

FIG. 12B is a see-through front view showing the mechanism as the thirdmodification, when viewed from the side of an internal gear member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawings, the present invention will now bespecifically described based on a preferred embodiment thereof.

As shown in FIGS. 1, 2A and 2B, a seat reclining mechanism according toone embodiment of the present invention is designed to be mounted to aseat cushion and a seat back of a seat so as to allow the seat back tobe reclined. The mechanism comprises a guide bracket 1 adapted to bemounted to the seat cushion, an internal gear member 2 adapted to bemounted to the seat back, four lock gear members 3, a rotatable cam 4, alock spring 5, a stopper plate 6, and a ring 7.

As shown in FIGS. 3A and 3B, the guide bracket 1 is formed in a circulardisk shape. The guide bracket 1 has a fitting portion which comprises afitting hole 1 a concentrically formed in the guide bracket 1. Thefitting hole 1 a includes a cutout 1 b formed to lock an outer end 5 aof the lock spring 5 which is a spiral spring.

The guide bracket 1 has four guide grooves 1 c which are formed in aninner surface thereof through a half blanking process to extend from aninner peripheral edge of the fitting hole 1 a in a radially outwarddirection of the guide bracket 1. The four guide grooves 1 c arearranged to form a cross shape, and the fitting hole 1 a is formed in acentral region of the guide grooves 1 c. The inner surface of the guidebracket 1 means a surface of the guide bracket 1 located in opposedrelation to the internal gear member 2.

Each of the guide grooves 1 c has a columnar-shaped convex portion 1 dformed through a half blanking process to protrude outwardly from anouter surface of the guide bracket 1. The convex portions 1 d serve as apositioning means to be used when the guide bracket 1 is mounted to theseat cushion.

The guide bracket 1 also has a semi-columnar-shapedforwardmost-inclination stopper protrusion 1 f and asemi-columnar-shaped rearwardmost-inclination stopper protrusion 1 gwhich are formed, respectively, in two regions defined between ahorizontally-extending right one and a downwardly-extending one of thefour guide grooves 1 c and between a horizontally-extending left one andthe downwardly-extending one of the four guide grooves 1 c in FIG. 3A,to protrude inwardly from the inner surface the guide bracket 1. Thesestopper protrusions 1 f, 1 g are formed through a half blanking process.The forwardmost-inclination stopper protrusion 1 f and therearwardmost-inclination stopper protrusion 1 g are adapted to come intocontact with the stopper plate 6 when the seat back is moved to aforwardmost inclined position and a rearwardmost inclined position,respectively, as will be described in detail later.

As shown in FIGS. 4A and 4B, the internal gear member 2 is formed in acircular disk shape. The internal gear member 2 is coupled to the guidebracket 1 in a rotatable manner about a rotation axis thereof withrespect to the guide bracket 1. The center of the guide bracket 1 islocated on the rotation axis of the internal gear member 2.

The internal gear member 2 has two steps of concave portions formed inan inner surface of thereof through a half blanking process. Twosidewalls constituting respective ones of the first-step concave portion2 k and the second-step concave portion 2 m are formed, respectively, ina circular shape and a circular arc shape in front view. Each of thecircular-shaped sidewall and the circular arc-shaped sidewall are formedin concentric relation with an after-mentioned through-hole 2 a. Theinner surface of the internal gear member 2 means a surface of theinternal gear member 2 located in opposed relation to the guide bracket1.

The sidewall of the first-step concave portion 2 k has internal teeth 2e formed over the entire inner peripheral surface thereof. The internalteeth 2 e are formed through a half blanking process.

The second-step concave portion 2 m has a bottom wall 2 b formed with athrough-hole 2 a having a diameter less than that of the fitting hole 1a of the guide bracket 1, and six columnar-shaped convex portions 2 ceach protruding outwardly from an outer surface of the internal gearmember 2, and four lock protrusions 2 d each protruding inwardly fromthe inner surface of the internal gear member 2. The through-hole 2 ahas a center located on the rotation axis of the internal gear member 2.The convex portions 2 c serve as a positioning means to be used when theinternal gear member 2 is mounted to the seat back. The lock protrusions2 d serve as a means to position and lock the stopper plate 6, as willbe described in detail later. Each of the convex portions 2 c and thelock protrusions 2 d are formed through a half blanking process.

The sidewall of the second-step concave portion 2 m is formed to have aninner peripheral surface which comprises a first free-zone arc portion 2f, a first lock-zone arc portion 2 h, a second free-zone arc portion 2g, and a second lock-zone arc portion 2 j. Each of the arc portions 2 f,2 h, 2 g, 2 j has a center located on the rotation axis of the internalgear member 2.

The first free-zone arc portion 2 f is located in opposed relation tothe second free-zone arc portion 2 g, and the first and second free-zonearc portions 2 f, 2 g are formed along a common circle. The firstlock-zone arc portion 2 h is located in opposed relation to the secondlock-zone arc portion 2 j, and the first and second lock-zone arcportions 2 h, 2 j are formed along a common circle.

The first free-zone arc portion 2 f has an arc length greater than thatof the second free-zone arc portion 2 g. That is, a center angle θ1 ofthe first free-zone arc portion 2 f is greater than a center angle θ2 ofthe second free-zone arc portion 2 g. Each of the free-zone arc portions2 f, 2 g has a curvature radius less than that of each of the lock-zonearc portions 2 h, 2 j.

The free-zone arc portions 2 f, 2 g are formed to allow anafter-mentioned protrusion 3 c of one of the lock gear members 3 to bein contact with either one thereof when the lock gear members 3 arelocated at a position where an after-mentioned external teeth 3 a of thelock gear members 3 are not in meshing engagement with the internalteeth 2 e of the internal gear member 2. Further, the lock-zone arcportions 2 h, 2 j are formed to allow the after-mentioned protrusion 3 cto be in contact with either one thereof when the lock gear members 3are located at a position where the after-mentioned external teeth 3 aare in meshing engagement with the internal teeth 2 e.

As shown in FIGS. 1, 2A and 2B, the four lock gear members 3 aredisposed between the guide bracket 1 and the internal gear member 2 toextend radially from the rotation axis in a cross-like pattern. That is,the four lock gear members are arranged at intervals of about 90degrees. This provides enhanced stability and safety in a locked state.

As shown in FIGS. 5A and 5B, each of the lock gear members 3 has anarc-shaped surface located in opposed relation to the internal teeth 2 eof the internal gear member 2 and formed with external teeth 3 ameshingly engageable with the internal teeth 2 e. Each of the lock gearmembers 3 is supported by a corresponding one of the guide grooves 1 cof the guide bracket 1 in such a manner as to be slidable in both a lockdirection R2 causing the external teeth 3 a to be brought into meshingengagement with the internal teeth 2 e and an unlock direction U2causing the external teeth 3 a to be released from the meshingengagement with the internal teeth 2 e. Each of the lock gear members 3has an engagement groove 3 b formed on a leading side of the unlockdirection U2 to allow a corresponding one of after-mentioned engagementpawls 4 e of the rotatable cam 4 to be brought into engagementtherewith. The engagement groove 3 b is formed in a shape which allowsthe after-mentioned engagement pawl 4 e to be inserted thereinto whenthe rotatable cam 4 is rotated in an after-mentioned unlock-causingrotation direction U1. As shown in FIG. 5A, one of the four lock gearmembers 3 has a protrusion 3 c protruding toward the internal gearmember 2. The protrusion 3 c is formed through a half blanking process.

As shown in FIGS. 1, 2A and 5C, the rotatable cam 4 is rotatablysupported by the fitting hole 1 a of the guide bracket 1, and adapted tobe rotatable in both a lock-causing rotation direction R1 and anunlock-causing rotation direction U1 illustrated in FIG. 5C. Therotatable cam 4 has a cam body 4 n, four engagement pawls 4 e protrudingfrom the cam body 4 n in the unlock-causing rotation direction U1, afitting boss 4 c protruding from the cam body 4 n toward the guidebracket 1, and a raised portion 4 m protruding from the fitting boss 4 ctoward the guide bracket 1.

The rotatable cam 4 has two steps of recesses concaved toward the guidebracket 1, when viewed from the side of the internal gear member 2. Therecesses are formed through a half blanking process. The fitting boss 4c is created by forming the first-step recess, and the raised portion 4m is created by forming the second-step recess.

The rotatable cam 4 has an elongate hole 4 a formed in a central regionthereof to have a shape close to an oval shape. The elongate hole 4 a isformed to penetrate through a bottom wall 4 b of the second-step recess.Each of the fitting boss 4 c, the raised portion 4 m and the elongatehole 4 a has a center located on the rotation axis of the internal gearmember 2.

The fitting boss 4 c has an annular-shaped boss body 4 j, and fourprotrusions 4 k which protrude radially from the boss body 4 j toward aninner peripheral surface of the fitting hole 1 a in a cross-likepattern, in such a manner that an outer peripheral surface of each ofthe protrusions 4 k comes into slide contact with the inner peripheralsurface of the fitting hole 1 a. In this manner, the fitting boss 4 c isfitted in (roughly guided by) the fitting hole 1 a under a conditionthat the respective outer peripheral surfaces of the protrusions 4 k arein contact with the inner peripheral surface of the fitting hole 1 a.This provides a centering function to the reclining mechanism so as toprevent axial wobbling of the rotatable cam 4 relative to the fittinghole 1 a.

For example, if the fitting boss 4 c consists only of an annular-shapedboss body, the boss body (i.e., the fitting boss 4 c) will be designedto have an outer diameter approximately equal to an inner diameter ofthe fitting hole 1 a in which the boss body is fitted. In this case, theouter diameter of the boss body is necessarily set at a value less thanan outer diameter of the cam body 4 n. By contrast, when the fittingboss 4 c comprises the boss body 4 j and the protrusions 4 k, and eachof the protrusions is formed to extend toward a root of a correspondingone of the engagement pawls 4 e, as in this embodiment, the fitting bosshas an outer diameter equal to a distance between the rotation axis andthe outer peripheral surface of each of the protrusions 4 k, so thateach of the outer diameter of the fitting boss 4 c and the innerdiameter of the fitting hole 1 a can be set at a value greater than theouter diameter of the cam body 4 n. This makes it possible to morestably rotate the rotatable cam 4 in its fitted state.

The raised portion 4 m is formed with a cutout 4 d for locking an innerend 5 b of the lock spring 5. The outer end 5 a of the lock spring 5 islocked by the cutout 1 b of the guide bracket 1, as mentioned above.Thus, the lock spring 5 biases the rotatable cam 4 in the lock-causingrotation direction R1.

An operation member, such as an operation rod connected to an operationlever or the like, penetrating through the fitting hole 1 a of the guidebracket 1 and the through-hole 2 a of the internal gear member 2, isfitted in the elongate hole 4 a in a non-rotatable manner relativethereto. Thus, the rotatable cam 4 can be rotated by the operationmember. The operation member is not supported by the guide bracket 1 andthe internal gear member 2.

The four engagement pawls 4 e are formed to protrude in a directionapproximately tangential to a circle having a center on the rotationaxis of the internal gear member 2, and arranged at approximately evenintervals.

As shown in FIGS. 5A, 5B and 5C, when the rotatable cam 4 is rotated inthe lock-causing rotation direction R1, the engagement pawls 4 e pushrespective outside walls 3 b 2 of the engagement grooves 3 b in the lockdirection R2. Thus, the lock gear members 3 are slidingly moved in thelock direction R2, so that the external teeth 3 a of the lock gearmembers 3 are brought into meshing engagement with the internal teeth 2e of the internal gear member 2 (see FIG. 6A).

When the rotatable cam 4 is rotated in the unlock-causing rotationdirection U1, the engagement pawls 4 a are brought into engagement withthe respective engagement grooves 3 b to pull respective inside walls 3b 1 of the engagement grooves 3 b in the unlock direction U2. Thus, thelock gear members 3 are slidingly moved in the unlock direction U2, sothat the external teeth 3 a of the lock gear members 3 are moved apartfrom the internal teeth 2 e of the internal gear member 2 to release themeshing engagement between the external teeth 3 a and the internal teeth2 e (see FIGS. 2B and 6B).

As shown in FIGS. 1, 7A and 7B, the stopper plate 6 is formed with fourcatch holes 6 a engageable with the respective lock protrusions 2 dprovided on the inner surface of the internal gear member 2. Thus, thestopper plate 6 is positioned and locked relative to the internal gearmember 2. The stopper plate 6 has a forwardmost-inclination stopperportion 6 b (see FIG. 7A) adapted to be brought into contact with theforwardmost-inclination stopper protrusion 1 f of the guide bracket 1when the seat back is moved to a forwardmost inclined position, and arearwardmost-inclination stopper portion 6 c (see FIG. 7B) adapted to bebrought into the rearwardmost-inclination stopper protrusion 1 g of theguide bracket 1 when the seat back is moved to a rearwardmost inclinedposition. The stopper portions 6 b, 6 c is formed by respectivecircumferentially opposite edges of an arc-shaped protrusion protrudingradially from a plate body 6 d of the stopper plate 6.

As above, the forwardmost-inclination stopper protrusion 1 f and therearwardmost-inclination stopper protrusion 1 g are formed in the guidebracket 1, and the stopper plate 6 is fixed to the internal gear member2, so that a stopper can be incorporated in the reclining mechanism.This makes it possible to prevent an increase in outside dimension of aseat so as to provide enhanced flexibility of seat layout. In addition,a need for a large-size stopper bracket can be eliminated to facilitatea reduction in weight of a seat.

The forwardmost-inclination stopper protrusion 1 f and therearwardmost-inclination stopper protrusion 1 g are formed in the guidebracket 1 through a half blanking process to facilitate a reduction incost. It is understood that each of the forwardmost-inclination stopperprotrusion 1 f and the rearwardmost-inclination stopper protrusion 1 gmay be prepared as a separate component. In this case, the stopperprotrusions 1 f, 1 g can be attached to the guide bracket 1 or theinternal gear member 2 after preparing the guide bracket 1 or theinternal gear member 2, so that a stopper position can be readilychanged in the event of design changes for a configuration or mountingposition of a reclining mechanism.

The ring 7 is fitted on an outer periphery of the guide bracket 1 andthe internal gear member 2 after the lock gear members 3, the rotatablecam 4, the stopper plate 6 are installed between the guide bracket 1 andthe internal gear member 2. In this manner, the reclining mechanism isunitized. The lock spring 5 can be installed from the fitting hole 1 aof the guide bracket 1 to allow the outer end 5 a and the inner end 5 bto be locked by the cutout 1 b of the guide bracket 1 and the cutout 4 dof the rotatable cam 4, respectively.

In a process of assembling the unitized reclining mechanism to a seat,the guide bracket 1 is mounted to a seat cushion, and the internal gearmember 2 is mounted to a seat back. Then, an operation member, such asan operation rod connected to an operation lever or the like, isinserted from the fitting hole 1 a of the guide bracket 1, and fitted inthe elongate hole 4 a of the rotatable cam 4 in a non-rotatable mannerrelative thereto.

A relationship between respective ones of the rotatable cam 4, the lockgear members 3, and the arc portions 2 f, 2 g, 2 h, 2 j of the internalgear member 2, will be described below.

Before the lock gear members 3 are brought into meshing engagement withthe internal gear member 2, the protrusion 3 c of one of the lock gearmembers 3 is brought into contact with either one of the free-zone arcportions 2 f, 2 g. When the protrusion 3 c is brought into contact witheither one of the free-zone arc portions 2 f, 2 g, the lock gear members3 are restrained, and thereby an unlocked state (lock-released state) ismaintained.

The first free-zone arc portion 2 f is used for a reclining mechanism ofa “type designed to keep a seat back from being locked at a forwardmostinclined position”. The second free-zone arc portion 2 g is used for areclining mechanism of a “type designed to lock a seat back at aforwardmost inclined position”.

As shown in FIG. 4A, the first free-zone arc portion 2 f has a centerangle greater than that of the second free-zone arc portion 2 g. Forexample, the center angle θ1 of the first free-zone arc portion 2 f isset at 106 degree, and the center angle θ2 of the second free-zone arcportion 2 g is set at 90 degree.

In a conventional seat reclining mechanism, an internal gear member isformed with only either one of the free-zone arc portions. Differently,in this embodiment, the internal gear member 2 is formed with both thefirst free-zone arc portion 2 f and the second free-zone arc portion 2g.

Thus, in an operation of installing the lock gear members 3 between theguide bracket 1 and the internal gear member 2, an installation positionof the protrusion 3 c of one of the lock gear members 3 can be selectedsuch that either one of the first free-zone arc portion 2 f and thesecond free-zone arc portion 2 g of the internal gear member 2 islocated relative to the protrusion 3 c. Thus, in this embodiment usingthe internal gear member 2, the installation position of the protrusion3 c can be changed to select either one of the type designed to keep aseat back from being locked at a forwardmost inclined position (i.e.,lock free type), and the type designed to lock a seat back at aforwardmost inclined position. This makes it possible to facilitate areduction in cost of the reclining mechanism.

FIGS. 8A and 8B are front views showing the reclining mechanism set asthe type designed to lock a seat back at a forwardmost inclinedposition, wherein FIG. 8A shows the reclining mechanism in a state whenthe seat back is at the forwardmost inclined position, and FIG. 8B showsthe reclining mechanism in a state when the seat back is at an initiallocked position (e.g., upright position) where it is initially lockedafter being inclined rearwardly from the forwardmost inclined position.

In this type, as the seat back is inclined forwardly from a rearwardlyinclined position, for example, from the state illustrated in FIG. 6B,the internal gear member 2 is rotated in a counterclockwise direction inFIG. 6B, and one edge of the second free-zone arc portion 2 g is movedbeyond the protrusion 3 c to allow the protrusion 3 c to be placed onthe first lock-zone arc portion 2 h. In conjunction with this movement,the restraint on movement of the lock gear members 3 in the lockdirection R2 is released, and thereby the lock gear members 3 areslidingly moved in the lock direction R2 to allow the external teeth 3 ato be brought into meshing engagement with the internal teeth 2 e. Thus,the seat back is locked at the forwardmost inclined position (the stateillustrated in FIG. 8A). In this state, the forwardmost-inclinationstopper portion 6 b of the stopper plate 6 is in contact with theforwardmost-inclination stopper protrusion 1 f of the guide bracket 1.

In an operation of inclining the seat back locked at the forwardmostinclined position rearwardly, the rotatable cam 4 is rotated in theunlock-causing rotation direction U1 using the operation member to allowthe engagement pawls 4 e of the rotatable cam 4 to be brought intoengagement with the respective engagement grooves 3 b of the lock gearmembers 3. Thus, the lock gear members 3 are slidingly moved along therespective guide grooves 1 c in the unlock direction U2, and thereby themeshing engagement between the external teeth 3 a and the internal teeth2 e is released, i.e., the locked state is released. Consequently, theinternal gear member 2 becomes rotatable relative to the guide bracket1.

In this lock-released state, when the seat back is inclined rearwardly,the protrusion 3 c placed on the first lock-zone arc portion 2 h ismoved in such a manner as to be placed on the second free-zone arcportion 2 g (the state illustrated in FIG. 6B). In the state when theprotrusion 3 c is in contact with the second free-zone arc portion 2 g,as shown in FIG. 6B, the movement of the lock gear members 3 in the lockdirection R2 is restrained. Thus, the seat back can be freely inclinedrearwardly or forwardly.

The seat back is further inclined rearwardly from the state illustratedin FIG. 6B, the other edge of the second free-zone arc portion 2 g ismoved beyond the protrusion 3 c to allow the protrusion 3 c to be placedon the second lock-zone arc portion 2 j. In conjunction with thismovement, the restraint on movement of the lock gear members 3 in thelock direction R2 is released, and thereby the lock gear members 3 areslidingly moved in the lock direction R2 to allow the external teeth 3 ato be brought into meshing engagement with the internal teeth 2 e. Thus,the seat back is locked at the initial locked position (e.g., uprightposition) (the state illustrated in FIG. 8B).

The seat back can be further inclined from the initial locked positionillustrated in FIG. 8B up to a rearwardmost inclined positionillustrated in FIG. 7B. During movement from the initial locked positionto the rearwardmost inclined position, the protrusion 3 c is placed onthe second lock-zone arc portion 2 j, and thereby the external teeth 4 ais in meshing engagement with the internal teeth 2 e, i.e., thereclining mechanism is in the locked state. Thus, in an operation ofinclining the seat back rearwardly from the initial locked position tothe rearwardmost inclined position, the rotatable cam 4 is rotated inthe unlock-causing rotation direction U1 using the operation member soas to slidingly move the lock gear members 3 in the unlock direction U2to release the locked state, and then the seat back is inclinedrearwardly.

When the seat back reaches the rearwardmost inclined position, therearwardmost-inclination stopper portion 6 c of the stopper plate 6 isbrought into contact with the rearwardmost-inclination stopperprotrusion 1 g of the guide bracket 1.

FIGS. 9A and 9B are front views showing the reclining mechanism set asthe type designed to keep the seat back from being locked at theforwardmost inclined position, wherein FIG. 9A shows the recliningmechanism in a state when the seat back is at the forwardmost inclinedposition, and FIG. 9B shows the reclining mechanism in a state when theseat back is at the initial locked position (e.g., upright position)where it is initially locked after being inclined rearwardly from theforwardmost inclined position.

In this type, the first free-zone arc portion 2 f having an arc lengthgreater than that of the second free-zone arc portion 2 g is used. Asthe seat back is inclined forwardly from a rearwardly inclined position,the internal gear member 2 is rotated. Then, when the seat back reachesthe forwardmost inclined position (the state illustrated in FIG. 9A),the protrusion 3 c is still placed on the first free-zone arc portion 2f. Thus, in this type, the seat back is not locked at the forwardmostinclined position. The remaining operations are the same as those in thetype designed to lock the seat back at the forwardmost inclinedposition, and their description will be omitted.

In the reclining mechanism according to the above embodiment, thefitting boss 4 c formed on the rotatable cam 4 is fitted in the fittinghole 1 a formed in the guide bracket 1. Alternatively, as shown in FIG.10, the rotatable cam 4 may be configured to have a plurality of (inthis modification, four) shaft-shaped protrusions 4 g formed atpositions to be in contact with the inner peripheral surface of thefitting hole 1 a, wherein the protrusions 4 g are fitted in the fittinghole 1 a. In this case, as long as each of the protrusions 4 g islocated on a common circle having a center on a rotation axis of therotatable cam 4 (i.e., on the rotation axis of the internal gear member2), the protrusions 4 g are not necessarily arranged at even intervals.Alternatively, in place of the plurality of protrusions, a disk-shapedraised portion having an outer peripheral surface fittable in the innerperipheral surface of the fitting hole 1 a as indicated by the two-dotchain line in FIG. 10 may be formed, wherein the raised portion isfitted in the fitting hole 1 a.

In place of the structure adapted to be fitted in the fitting hole 1 a,a recess 1 h adapted to come into circumscribing contact with theengagement pawls 4 e of the rotatable cam 4 may be formed in the innersurface of the guide bracket 1, wherein respective outer peripheralportions of the engagement pawls 4 e of the rotatable cam 4 are fittedin an inner peripheral surface of the recess 1 h, as shown in FIGS. 11Aand 11B. In this manner, an outer peripheral portion of the rotatablecam 4 is fitted in the fitting recess 1 h, so that the rotatable cam 4can be stably rotated in its fitted state.

Further, in place of the structure adapted to be fitted in the fittinghole 1 a, a plurality of (in this modification, four) shaft-shapedprotrusions 1 j may be formed on the inner surface of the guide bracket1 in such a manner as to come into contact with an outer peripheralsurface of a circular plate 20 which is formed with a plurality ofengagement holes 20 a and a center hole 20 b, and disposed between theguide bracket 1 and the internal gear member 2, as shown in FIGS. 12Aand 12B. In this case, the rotatable cam 4 is formed with a plurality of(in this modification, four) shaft-shaped protrusions 4 h. Theprotrusions 4 h are inserted into the respective engagement holes 20 aof the circular plate 20 to allow the circular plate 20 to be integratedwith the rotatable cam 4. The operation member is inserted into thecenter hole 20 b of the circular plate 20. As long as each of theprotrusions 1 j is located on a circle concentric with the circularplate 20, the protrusions 1 j are not necessarily arranged at evenintervals. In this manner, the circular plate 20 integral with therotatable cam 4 is fitted inside the protrusions 1 j, so that therotatable cam 4 can be stably rotated in its fitted state.

While the above embodiment has been described based on one example wherethe guide bracket and the internal gear member are mounted,respectively, to the seat cushion and the seat back, the internal gearmember and the guide bracket may be mounted, respectively, to the seatcushion and the seat back.

Further, while the above embodiment has been described based on oneexample where the four lock gear members are arranged, the number of thelock gear members may be two or three or may be five or more.

The above embodiment may be summarized as follows.

According to one aspect of the present invention, there is provided aseat reclining mechanism designed to be mounted to a seat cushion and aseat back so as to allow the seat back to be reclined. The seatreclining mechanism comprises: a guide bracket adapted to be mounted toeither one of the seat cushion and the seat back; an internal gearmember adapted to be mounted to a remaining one of the seat cushion andthe seat back, wherein the internal gear member is coupled to the guidebracket in a rotatable manner about a rotation axis thereof with respectto the guide bracket, and formed with internal teeth along a circlehaving a center on the rotation axis; a plurality of lock gear membersdisposed between the guide bracket and the internal gear member toextend radially from the rotation axis, wherein each of the lock gearmembers is formed with external teeth meshingly engageable with theinternal teeth, and supported by the guide bracket in such a manner asto be slidable in both a lock direction causing the external teeth to bebrought into meshing engagement with the internal teeth and an unlockdirection causing the external teeth to be released from the meshingengagement with the internal teeth; a fitting portion provided in eitherone of the guide bracket and the internal gear member; a rotatable camrotatably supported by the fitting portion, and adapted to be rotatablein both a lock-causing rotation direction causing the lock gear membersto be slidingly moved in the lock direction and an unlock-causingrotation direction causing the lock gear members to be slidingly movedin the unlock direction; and a lock spring biasing the rotatable cam inthe lock-causing rotation direction.

In the seat reclining mechanism of the aspect of the present invention,the rotatable cam is fitted in (roughly guided by) the fitting portionprovided in either one of the guide bracket and the internal gearmember, so that the rotatable cam is rotatably supported within thereclining mechanism. This makes it possible to stably perform alock/unlock operation between the guide bracket and the internal gearmember. In addition, a centering function is incorporated in thereclining mechanism to eliminate a need for an operation rod and abearing member with a high degree of dimensional accuracy, so thatcentering of the rotatable cam can be achieved at a low cost.

Preferably, the fitting portion comprises a fitting hole formed ineither one of the guide bracket and the internal gear member, and therotatable cam has a fitting boss adapted to be fitted into the fittinghole.

According to this feature, the fitting boss of the rotatable cam isfitted in the fitting hole. This makes it possible to stably rotate therotating cam in its fitted state.

Preferably, the fitting boss has an annular-shaped boss body, and aplurality of protrusions which protrude radially from the boss bodytoward an inner peripheral surface of the fitting hole to come intoslide contact with the inner peripheral surface.

According to this feature, a total diameter of the plurality ofprotrusions can be increased while minimizing a diameter of the bossbody of the fitting boss, so as to more stably rotate the rotating camin its fitted state.

Alternatively, the fitting portion may comprise a fitting recess formedin either one of the guide bracket and the internal gear member, and therotatable cam has an outer peripheral portion fitted into the fittingrecess.

According to this feature, the outer peripheral portion of the rotatablecam is fitted in the fitting recess. This makes it possible to stablyrotate the rotating cam in its fitted state.

Preferably, the seat reclining mechanism of the aspect of the presentinvention further comprises a circular plate disposed between the guidebracket and the internal gear member, and integrated with the rotatablecam, wherein the fitting portion is formed in either one of the guidebracket and the internal gear member to have a plurality of protrusionsdisposed along an outer periphery of the circular plate.

According to this feature, the circular plate integrated with therotatable cam is fitted inside the plurality of protrusions. This makesit possible to stably rotate the rotating cam in its fitted state.

Preferably, in the seat reclining mechanism of the aspect of the presentinvention, the rotatable cam has a cam body, and a plurality ofengagement pawls disposed on a circumference of a circle having a centeron the rotation axis and each formed to protrude from the cam body inthe lock-causing rotation direction or the unlock-causing rotationdirection, and the plurality of lock gear members are formed,respectively, with a plurality of engagement grooves engageable withrespective ones of the plurality of engagement pawls, wherein, when therotatable cam is rotated in the lock-causing rotation direction, theengagement pawls push the respective engagement grooves in the lockdirection to allow the lock gear members to be slidingly moved in thelock direction, and, when the rotatable cam is rotated in theunlock-causing rotation direction, the engagement pawls pull therespective engagement grooves in the unlock direction to allow the lockgear members to be slidingly moved in the unlock direction.

According to this feature, when the rotatable cam is rotated in thelock-causing rotation direction, the engagement pawls push therespective engagement grooves in the lock direction, so that the lockgear members are slidingly moved in the lock direction. Thus, theexternal teeth are brought into meshing engagement with the internalteeth. Then, when the rotatable cam is rotated in the unlock-causingrotation direction, the engagement pawls are brought into engagementwith respective engagement grooves in such a manner as to pull theengagement grooves in the unlock direction, so that the lock gearmembers are slidingly moved in the unlock direction. Thus, the externalteeth are moved apart from the internal teeth to release the meshingengagement between the external teeth and the internal teeth. This makesit possible to eliminate a conventional need for providing a circularlever (actuating plate) for moving the lock gear members in the unlockdirection, as a separate component, so as to facilitate a reduction incost. In addition, the reclining mechanism can be reduced in overallthickness by eliminating the circular lever.

1. A seat reclining mechanism designed to be mounted to a seat cushionand a seat back so as to allow said seat back to be reclined, said seatreclining mechanism comprising: a guide bracket adapted to be mounted toeither one of said seat cushion and said seat back; an internal gearmember adapted to be mounted to a remaining one of said seat cushion andsaid seat back, said internal gear member being coupled to said guidebracket in a rotatable manner about a rotation axis thereof with respectto said guide bracket, and formed with internal teeth along a circlehaving a center on said rotation axis; a plurality of lock gear membersdisposed between said guide bracket and said internal gear member toextend radially from said rotation axis, each of said lock gear membersbeing formed with external teeth meshingly engageable with said internalteeth, and supported by said guide bracket in such a manner as to beslidable in both a lock direction causing said external teeth to bebrought into meshing engagement with said internal teeth and an unlockdirection causing said external teeth to be released from the meshingengagement with said internal teeth; a fitting portion provided ineither one of said guide bracket and said internal gear member; arotatable cam rotatably supported by said fitting portion, and adaptedto be rotatable in both a lock-causing rotation direction causing saidlock gear members to be slidingly moved in said lock direction and anunlock-causing rotation direction causing said lock gear members to beslidingly moved in said unlock direction; and a lock spring biasing saidrotatable cam in said lock-causing rotation direction, wherein: saidfitting portion comprises a fitting hole formed in said either one ofsaid guide bracket and said internal gear member, said rotatable cam hasa fitting boss adapted to be fitted into said fitting hole, said fittingboss has an annular-shaped boss body, and a plurality of protrusionsthat protrude radially from said boss body toward an inner peripheralsurface of said fitting hole to come into sliding contact with saidinner peripheral surface.
 2. The seat reclining mechanism as defined inclaim 1, wherein: said rotatable cam has a cam body, and a plurality ofengagement pawls disposed on a circumference of a circle having a centeron said rotation axis and each formed to protrude from said cam body insaid lock-causing rotation direction or said unlock-causing rotationdirection; and said plurality of lock gear members are formed,respectively, with a plurality of engagement grooves engageable withrespective ones of said plurality of engagement pawls, wherein, whensaid rotatable cam is rotated in said lock-causing rotation direction,said engagement pawls push said respective engagement grooves in saidlock direction to allow said lock gear members to be slidingly moved insaid lock direction, and, when said rotatable cam is rotated in saidunlock-causing rotation direction, said engagement pawls pull saidrespective engagement grooves in said unlock direction to allow saidlock gear members to be slidingly moved in said unlock direction.